Effects of surface morphology on enhanced photoelectrochemical properties of nanocrystals Elizabeth Donoway

Solar Technology• Current silicon-based solar panels

• Expensive• Inefficient• Prone to damage

• Silicon sheeted panels• Unstable• Large band gap• Low energy output• Small surface area

Gupta, S. et al., 2013

Nanocrystals• Larger surface area to volume ratio• Regulated manipulation of characteristics• Unique electrochemical properties• Multi-faceted nanocrystals

• Configuration and structure determine stability• {100}-bound cubes• {111}-bound octahedrons

Yang, Y. et al., Nanoscale, 2014, 6, 4316

New Solar Materials

• Cuprous oxide (Cu2O)• Efficient• Inexpensive• Small band gap• Unstable

• Polyvinylpyrrolidone (PVP)• Capping molecule• Stabilization of crystals

Zhang, D. F. et al., Journal of Materials Chemistry, 2009, 19(29), 5220-5225.

Van de Krol, R. et al., Journal of Materials Chemistry, 2008, 18(20), 2311-2320

Purpose• Determine the effects of surface morphology on

nanocrystal stability

• Fabricate Cu2O nanocrystals that are stable in solution

• Optimize nanocrystal morphology to create efficient materials for use in solar reactions

Methods• Nanocrystal Synthesis

• Seeding of crystals from copper (II) chloride• Addition of PVP to form octahedrons by truncating cube vertices

• Characterization• TEM/SEM Imaging

• Electrode Preparation• Adhesion of nanocrystals to FTO glass slides

• Photoelectrochemical Assays• Controlled Potential Electrolysis (CPE)

• Determines electrode stability• External Quantum Efficiency (EQE)

• Determines wavelengths of light that the solar panel is optimized for use in• Solar Cell Efficiency

•

Results – Characterization

Cu2O Nanocubes

Cu2O Nanooctahdrons

Cu2O Nanocubes

Cu2O Nanooctahedrons

Results – Characterization• Both nanocubes and nanocrystals were successfully fabricated• TEM/SEM imaging confirmed that sizes and shapes of nanocrystals were differentiated, preventing agglomeration and sheeting, which would lower efficiency and reduce surface area available for light reactions to occur

Results – Controlled Potential Electrolysis (Nanocubes)

Single deposition of Cu2O nanocubes on FTO glass (average of 40 trials). CPE was conducted at increased energies equivalent to those exposed over a typical solar panel lifetime, corresponding to decades of solar cell use. Electrode samples were irradiated with solar light during two five-minute periods, alternating light and dark conditions in five second intervals.

Dark DarkLight Light

Results – Controlled Potential Electrolysis (Nanocubes)

Single deposition of Cu2O nanocubes on FTO glass during light irradiation intervals. Light and dark conditions were alternated in five second intervals to ensure that electrodes remained stable during large fluctuations in photonic energy. Baseline photocurrent density (J) remained constant between solar irradiation periods during electrolysis. The obtention of photocurrent density away from the zero value during light irradiation over all 40 trials indicated maintained stability of electrodes.

Light on

Light off

Results – Controlled Potential Electrolysis (Nanooctahedrons)

Single deposition of Cu2O nanooctahedrons on FTO glass (average of 40 trials). Electrode samples were irradiated with solar light during two five-minute periods, alternating light and dark conditions in five second intervals. Exponential increase in magnitude of photocurrent density during light conditions indicates increased photocatalytic activity in nanooctahedron electrodes.

Light LightDarkDark

Results – Controlled Potential Electrolysis (Nanooctahedrons)

Single deposition of Cu2O nanooctahedrons on FTO glass. Baseline remained constant between solar irradiation periods during electrolysis. Increase in photocurrent density magnitude away from the zero in all trials indicates maintained stability and increased photocatalytic response.

Light off

Light on

Results – External Quantum Efficiency

External quantum efficiency expressed as a percentage of photons absorbed and converted into electric current, modeled as a function of wavelength (nm). The longer range of wavelengths for which both Cu2O nanocrystal panels achieve 100% external quantum efficiency compared to Si-based cells indicates their optimization for use in the solar emission spectrum.

[ ]Si-based

Results – Solar Cell Efficiency

• Cu2O Electrode Efficiency• ηmax,theoretical =86%

• Cu2O Nanocube Efficiency• Pmax=107.2 mW• ηexperimental=53.6%

• Cu2O Nanooctahedron Efficiency• Pmax=125.4 mW• ηexperimental=62.7%

• Silicon Panel Efficiency• ηmax,theoretical=29%• ηmax,experimental=21.5%

Discussion• Stability

• Stabilization of Cu2O via morphological manipulation of nanocrystals• Both nanocubes and nanooctahedrons remained stable

• Photocurrent density magnitude increase in light condition• 11 μA cm-2 difference in magnitude between octahedron and cube electrodes

• Efficiency• Nanocrystals optimized for use in solar emission spectrum• Different morphologies demonstrate varied electrochemical properties

• Nearly 200% increase in efficiency over Si-based cells• Applications

• Addresses instability of current materials• New, inexpensive solar technologies made from Cu2O

• Cu2O cells are half as expensive to produce as Si-based cells

Future Research• Assessment of photovoltaic cell performance and resistance to degradation under environmental conditions• More specific evaluation of nanooctahedron morphology to further optimize nanocrystals for use in solar panels and increase panel efficiency• Stabilization of alternate materials (e.g. graphene, germanium arsenide, titanium dioxide) for use in solar panels

Acknowledgements• Joseph DuChene• Dr. Wei David Wei• Wei Research Group• Student Science Training Program• Pine Crest School• Sigma Xi

References• Borgohain, K., Murase, N., & Mahamuni, S. (2002). Synthesis and properties of Cu2O quantum particles. Journal of applied physics, 92(3), 1292-1297. • De Jongh, P. E., Vanmaekelbergh, D., & Kelly, J. J. D. (2000). Photoelectrochemistry of Electrodeposited Cu2 O. Journal of The Electrochemical Society, 147(2), 486-489. • Ho, J. Y., & Huang, M. H. (2009). Synthesis of submicrometer-sized Cu2O crystals with morphological evolution from cubic to hexapod structures and their comparative photocatalytic activity. The Journal of Physical Chemistry C,113(32), 14159-14164. • Hua, Q., Shang, D., Zhang, W., Chen, K., Chang, S., Ma, Y., ... & Huang, W. (2010). Morphological evolution of Cu2O nanocrystals in an acid solution: stability of different crystal planes. Langmuir, 27(2), 665-671. • Huang, W. C., Lyu, L. M., Yang, Y. C., & Huang, M. H. (2011). Synthesis of Cu2O nanocrystals from cubic to rhombic dodecahedral structures and their comparative photocatalytic activity. Journal of the American Chemical Society,134(2), 1261-1267. • Huang, X., Chen, Y., Chiu, C. Y., Zhang, H., Xu, Y., Duan, X., & Huang, Y. (2013). A versatile strategy to the selective synthesis of Cu nanocrystals and the in situ conversion to CuRu nanotubes. Nanoscale, 5(14), 6284-6290. • Jiao, Y., Jiang, H., & Chen, F. (2014). RuO2/TiO2/Pt ternary photocatalysts with epitaxial heterojunction and their application in CO oxidation. ACS Catalysis. • Kuo, C. H., & Huang, M. H. (2008). Facile synthesis of Cu2O nanocrystals with systematic shape evolution from cubic to octahedral structures. The Journal of Physical Chemistry C, 112(47), 18355-18360. • Paracchino, A., Laporte, V., Sivula, K., Gratzel, M., & Thimsen, E. (2011). Highly active oxide photocathode for photoelectrochemical water reduction. Nature materials, 10(6), 456-461. • Sowers, K. L., & Fillinger, A. (2009). Crystal face dependence of p-Cu2O stability as photocathode. Journal of The Electrochemical Society, 156(5), F80-F85. • Susman, M. D., Feldman, Y., Vaskevich, A., & Rubinstein, I. (2014). Chemical Deposition of Cu2O Nanocrystals with Precise Morphology Control. ACS nano,8(1), 162-174. 19 • Tsai, Y. H., Chiu, C. Y., & Huang, M. H. (2013). Fabrication of Diverse Cu2O Nanoframes through Face-Selective Etching. The Journal of Physical Chemistry C, 117(46), 24611-24617. • Vilhelmsen, L. B., & Hammer, B. (2014). Identification of the Catalytic Site at the Interface Perimeter of Au Clusters on Rutile TiO2 (110). ACS Catalysis. • Wang, Y. C., DuChene, J. S., Huo, F., & Wei, W. D. (2014). An in situ Approach for Facile Fabrication of Robust and Scalable SERS Substrates.Nanoscale. • Xu, Y., Wang, H., Yu, Y., Tian, L., Zhao, W., & Zhang, B. (2011). Cu2O Nanocrystals: Surfactant-Free Room-Temperature Morphology-Modulated Synthesis and Shape- Dependent Heterogeneous Organic Catalytic Activities.The Journal of Physical Chemistry C, 115(31), 15288-15296. • Zhang, D. F., Zhang, H., Guo, L., Zheng, K., Han, X. D., & Zhang, Z. (2009). Delicate control of crystallographic facet-oriented Cu 2 O nanocrystals and the correlated